A lawyer in civilian life, he had been decorated for counterespionage and counterterrorism work during 22 years as a reserve Army intelligence officer in which he rose to the rank of lieutenant colonel. His posting, just as the Guantánamo hearings were accelerating in 2004, gave him a close-up view of the government’s detention policies.

It also turned him into one of the Bush administration’s most unlikely adversaries.

In June, Colonel Abraham became the first military insider to criticize publicly the Guantánamo hearings, which determine whether detainees should be held indefinitely as enemy combatants. Just days after detainees’ lawyers submitted an affidavit containing his criticisms, the United States Supreme Court reversed itself and agreed to hear an appeal arguing that the hearings are unjust and that detainees have a right to contest their detentions in federal court.

Some lawyers say Colonel Abraham’s account — of a hearing procedure that he described as deeply flawed and largely a tool for commanders to rubber-stamp decisions they had already made — may have played an important role in the justices’ highly unusual reversal. That decision once again brought the administration face to face with the vexing legal, political and diplomatic questions about the fate of Guantánamo and the roughly 360 men still held there.

“Nobody stood up and said the emperor’s wearing no clothes,” Colonel Abraham said in an interview. “The prevailing attitude was, ‘If they’re in Guantánamo, they’re there for a reason.’ ”

The curtain on the hearings had been pulled back a bit previously, when the Pentagon, under pressure, released some transcripts. But by stepping forward, Colonel Abraham gave the Supreme Court and the public a look from an insider at a process that remains heavily shielded.

He expanded on that account in a series of recent conversations at his law office here, offering a detailed portrait of a system that he described as characterized by superficial efforts to gather evidence and frenzied pressure to conduct hundreds of hearings in a few months.

Most detainees, he said, have no realistic way to contest charges often based not on solid information, but on generalizations, incomplete intelligence reports and hints of terrorism ties.

“What disturbed me most was the willingness to use very small fragments of information,” he said, recounting how, over his six-month tour, he grew increasingly uneasy at what he saw. In the interviews, he often spoke coolly, with the detachment of a lawyer, but as time wore on grew agitated as he described his experiences.

Often, he said, intelligence reports relied only on accusations that a detainee had been found in a suspect area or was associated with a suspect organization. Some, he said, described detainees as jihadist without detail.

Pentagon officials have dismissed his criticisms as biased and said he was not in the position to have seen the entire process work.

As an intelligence officer responsible for running the central computer depository of evidence for the hearings, he said, he saw many of the documents in hundreds of the 558 cases. He also worked as a liaison with intelligence agencies and served on one three-member hearing panel.

All of which has left Colonel Abraham, 46, a civilian business lawyer who has lately been busy with a lawsuit between makers of pomegranate juice, with a central role in the public debate over Guantánamo. His account has been widely discussed in Congress, the administration and the press. On Friday, a federal appeals court judge took note of it in describing what she said were problems with the Pentagon’s hearing process.

He has been called a whistleblower and a traitor. On July 26, he is to testify before a House committee.

His road to notoriety, he says, is entirely of a piece with his biography. A political conservative who says he cried when Richard M. Nixon resigned the presidency, he says he has remained a reservist throughout his adult life to repay the country for the opportunities it offered his family. His father is a Holocaust survivor who emigrated after the Second World War.

“It is my duty,” Colonel Abraham said of his decision to come forward.

Pentagon officials say his account indicates that he misunderstood the purpose of the hearings, known as combatant status review tribunals or C.S.R.T.’s, which the officials say “afford greater protections for wartime detainees than any nation has ever provided.”

A Pentagon spokesman, Lt. Cmdr. Chito Peppler of the Navy, said that Colonel Abraham’s “apparently biased insinuations” did not indicate bad faith or improper behavior by military officials.

“In his capacity as database manager during his brief stint on active duty several years ago,” Commander Peppler said, “Lieutenant Colonel Abraham was not in a position to have a complete view of all the evidence used in the C.S.R.T.’s, as well as the process as a whole.”

Colonel Abraham arrived at the Office for the Administrative Review of the Detention of Enemy Combatants during a chaotic period in September 2004.

The plan for the hearings had come from the highest levels of the Pentagon after two Supreme Court rulings on June 28, 2004, put the Bush administration on the defensive over its detainee policies.

One ruling suggested that detainees would be entitled to hearings “before a neutral decision maker.” The other said detainees could have federal courts review their detentions. Nine days later, Paul D. Wolfowitz, then deputy defense secretary, issued an order creating the C.S.R.T.’s.

Colonel Abraham had already served a year on active duty after the 2001 terrorist attacks. At Pearl Harbor, he had been cited for exceptionally meritorious service as “lead counterterrorism analyst,” burnishing a record that included a citation for leading a counterespionage operation in the 1980s that ended with the detention of three Soviet agents.

A divorced father of a 7-year-old daughter, he was not looking for a posting. But a commander suggested that his skills were needed: the hearing program was entering its busiest period, with more than 200 people gathering evidence and running the hearings at an office near the Pentagon and in Guantánamo.

It was obvious, Colonel Abraham said, that officials were under intense pressure to show quick results. Quickly, he said, he grew concerned about the quality of the reports being used as evidence. The unclassified evidence, he said, lacked the kind of solid corroboration he had relied on throughout his intelligence career. “The classified information,” he added, “was stripped down, watered down, removed of context, incomplete and missing essential information.”

Many detainees implicated other detainees, he said, and there was often no way to test whether they had provided false information to win favor with interrogators.

He said he was prohibited from discussing the facts of cases. But public information, much of it obtained through lawsuits, includes examples of some of the points he made.

In a hearing on Oct. 26, 2004, a transcript shows, one detainee was told that another had identified him as having attended a terrorism training camp.

The detainee asked that his accuser be brought to testify. “We don’t know his name,” the senior officer on the hearing panel said.

At another hearing, later reviewed by a federal judge, a Turkish detainee, Murat Kurnaz, was said to have been associated with an Islamic missionary group. He had also traveled with a man who had become a suicide bomber.

“It would appear,” Judge Joyce Hens Green wrote in 2005, “that the government is indefinitely holding the detainee — possibly for life — solely because of his contacts with individuals or organizations tied to terrorism and not because of any terrorist activities that the detainee aided, abetted or undertook himself.”

In a third hearing, an Afghan detainee said he had indeed been a jihadist — during the 1980s war against the Soviet Union, when a lot of Afghans were jihadists. Was that what the accusation against him meant, he asked, or was it referring to later, during the American war?

“We don’t know what that time frame was, either,” the tribunal’s lead officer replied.

During one of the recent interviews, Colonel Abraham said that the general accusations that detainees were jihadists without much more alarmed him.

“As an intelligence agent, I would have written ‘junk statement’ across that,” he said.

Critics of the administration’s detention policies have questioned the hearings’ fairness, noting that detainees are not permitted lawyers and cannot see much of the evidence. Pentagon officials have said such criticism is not meaningful because a combatant status hearing “is not a criminal trial.” They note that 38 of the 558 cases ended in decisions favorable to the detainees.

But Colonel Abraham said that in meetings with top officials of the office, it was clear that such findings were discouraged. “Anything that resulted in a ‘not enemy combatant’ would just send ripples through the entire process,” he said. “The interpretation is, ‘You got the wrong result. Do it again.’ ”

He said his concerns about the fairness of the hearings had grown as time passed. “The hearings amounted to a superficial summary of information, the quality of which would not have withstood scrutiny in any serious law-enforcement or intelligence investigation,” he said.

While in Washington, he stayed with a sister, Susan J. Borschel, a real estate lawyer. Last week, she recalled Colonel Abraham’s saying that he was troubled by the way the Pentagon was running the hearings. It was a notable observation, she said, from a “law and order” man.

Soon, Colonel Abraham said in one of the conversations, he began to worry that involvement in the process might be improper for a lawyer because there were so many shortcuts. “There were too many assumptions. Too many presumptions,” he said. He said he had expressed his concerns to supervising officers.

His law partner, Steven Fink, said that would not have been unusual. “You will get his opinion whether you want it or not,” Mr. Fink said.

Colonel Abraham’s misgivings reached a peak in December 2004.

On Dec. 10, he wrote a letter to Rear Adm. James M. McGarrah, who was running the hearings operation. In the letter, a copy of which he provided to The New York Times, Colonel Abraham asked to be released from his assignment, saying participation “may be in conflict with my obligations as an attorney.” He said he had never received an official response.

He finished his tour, which ended in March. He came back to his life in Newport Beach and, he said, more or less forgot about Guantánamo.

As it turned out, lawyers at his sister’s firm, Pillsbury Winthrop Shaw Pittman, began representing detainees in 2006. Though she is not involved, she mentioned that her brother had worked on the hearings.

Last month, one of the lawyers, Matthew J. MacLean, a former Army lawyer, called Colonel Abraham and asked him to look at an affidavit filed in May by Admiral McGarrah.

Colonel Abraham said the admiral’s affidavit, describing the hearing process as orderly and considered, had convinced him that he had to step forward. He began to describe his experience.

“This was it,” Mr. MacLean said last week, “the first evidence of how these tribunals operated from the inside.”

Mr. MacLean called Colonel Abraham for the first time on June 8. The detainees’ lawyers filed his seven-page affidavit in court on June 22. It was sharply critical of the hearings and the evidence they used, saying “what purported to be specific statements of fact lacked even the most fundamental earmarks of objectively credible evidence.” On June 29, the Supreme Court announced that it would hear the detainees’ case.

One of the tribunals the lawyers have learned more about since then was the one on which Colonel Abraham sat. Documents they have gathered show that he was assigned to the panel in November 2004. The detainee was a Libyan, captured in Afghanistan, who was said to have visited terrorist training camps and belonged to a Libyan terrorist organization.

By a vote of 3 to 0, the panel found that “the detainee is not properly classified as an enemy combatant and is not associated with Al Qaeda or Taliban.”

Two months later, apparently after Pentagon officials rejected the first decision, the detainee’s case was heard by a second panel. The conclusion, again by a vote of 3 to 0, was quite different: “The detainee is properly classified as an enemy combatant and is a member of or associated with Al Qaeda.”

Colonel Abraham was never assigned to another panel.

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